We have continued to study the function and regulation of the polyamines in the eukaryote Saccharomyces cerevisiae utilizing biochemical and genetic techniques. We have emphasized four aspects of the overall problem. (1) We have cloned the gene that codes for adenosylmethionine decarboxylase, an essential enzyme in the pathway to spermidine and spermine. This enzyme, like the Escherichia coli enzyme, contains the novel covalently-linked cofactor pyruvate. (2) We have demonstrated a role for the polyamines in the cell cycle of an ornithine decarboxylase-deficient mutant of yeast. By phase microscopy and fluorescent staining, we have shown that the budded forms that accumulate in polyamine-deficient cells have completed nuclear synthesis and separation. However, cytokinesis does not take place, and the mother and daughter cells fail to separate. Arrest is therefore not in G1, as is usual for cells deficient in other auxotrophic requirements. Thus, the ornithine decarboxylase-deficient mutant can be classified as a cell division cycle mutant. (3) We have shown in preliminary mapping studies that the gene for ornithine decarboxylase maps on chromosome 2. (4) We have continued our studies on the regulation of the spel gene (for ornithine decarboxylase) and the bypass mutant SPE40 which lacks spermine synthase and was isolated during prolonged incubation of the spel strain in the absence of amines. SPE40 restores ornithine decarboxylase activity to the spel-mutants. We have carried out mating and tetrad analysis and shown that these two genes are not separable by standard genetic techniques. We have also shown definitively that the mutant SPE40 is dominant.